LTE Advanced coordinated multipoint, CoMP, is used to send and receive data to and from a wireless device or user equipment, UE, from several points.
LTE Coordinated Multipoint is essentially a range of different techniques that enable the dynamic coordination of transmission and reception over a variety of different base stations. The aim is to improve overall quality for the user as well as improving the utilisation of the network. LTE Advanced CoMP turns the inter-cell interference, ICI, into useful signal, especially at the cell borders where performance may be degraded.
LTE CoMP, Coordinated Multipoint requires coordination between several of geographically separated base stations or evolved Node B:s, eNB. In CoMP the eNB:s dynamically coordinate their transmissions to provide joint scheduling and transmissions, as well as proving joint processing of the received signals. In this way a UE at the edge of a cell is able to be served by two or more eNBs to improve signals reception/transmission and increase throughput particularly under cell edge conditions.
Currently in 3GPP, several downlink, DL, CoMP modes are being discussed and will be included into the specification. Compared to the coherent Joint TX, which has been available in previous 3GPP releases, these CoMP modes have benefits that a tight synchronization between cooperative points is not mandatory so that the network implementation and deployment cost can be significantly reduced. However, the DL LTE CoMP modes require dynamic coordination amongst several geographically separated eNBs transmitting to the UE.
In contrast of uplink, UL, CoMP, where the signal and link quality could be measured at the base station or access point sides, DL CoMP needs sufficient and accurate quality measurement and report support at the UE sides. Some of these might not be available or not standard compatible. Hence, DL CoMP might be more difficult to get gains if information is hard to obtain or inaccurate, due to the aforementioned reasons. Furthermore, after the deployment of 3GPP-4G release 11 networks, there will still be a high ratio of legacy i.e. 3GPP-4G release 8-10 UEs.
Legacy UE only measures the Channel State Information, CSI, for a single link from its serving point. Therefore, the DL comp modes are not enabled for these legacy UEs.